Printer page description languages (PDL), such as Postscript (a trademark of Adobe Systems Incorporated), use opaque image build up techniques to create the print page image. As new subimages are added to the image, the new subimage is written over the previous image within the boundary of the new subimage. These subimages are two dimensional regions which are mapped into memory space and stored until the image creation is complete. This requires an image memory which is either addressable on display element boundaries or a memory which can be read, modified, and rewritten. The former requires image processors with narrow data bus widths which are not conducive to high speed data transfers. The latter allows for high speed transfers but requires transfer of data which may not need to be modified.
These images consist of relatively few bits per display element but high performance processors necessary to process this type of image typically have data busses with widths which are several times wider than the number of bits in a display element.